Open-loop scrubbers, science and the Japan report

The ongoing debate about open-loop scrubbers often drifts towards being a clash of personalities and organisations (including lobby groups) whereas in my opinion we should be discussing in a rational manner, what adverse impact (if any) open-loop scrubbers may have on the marine environment.

“For a successful technology, reality must take precedence over public relations, for nature cannot be fooled.” - Richard Feynman.

When it comes to shipping though quite often any discussion about science or technology is limited to people with no background in science or technology, telling us what their opinion is.

Logical fallacies particularly variations of argumentum ad verecundiam (appeal to authority) are also utilised and we are supposedly expected to accept the claims of a person if they hold a senior position, or of an organisation because they are “trusted”, even without sufficient evidence to support what they claim is accurate. That however is not how the scientific method works or to quote Galileo Galilei, “In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual."Views regarding open-loop scrubbers vary, but generally they follow two broad narratives. One is that they reduce emissions and don’t harm the marine environment, with the alternative or opposing narrative being that discharge water from scrubbers is basically pollution. Most parties involved in the debate agree though that scrubbers do reduce harmful airborne emissions including particulate matter. So in that respect they might be a step in the right direction.

My interest in this topic was begrudgingly renewed when I saw headlines recently in the shipping media heralding that Japan had basically declared open-loop scrubbers safe for the marine environment. One shipping publication even led its story with the headline “Japan tells IMO scrubbers are safe”. Around this time I also came across a very interesting post on LinkedIn by a Hong Kong based doctoral student, Surinder Brrar, about the report behind these headlines.

Mr. Brrar was concerned enough after reading: Report by the expert board for the environmental impact assessment of discharge water from Scrubbers (Japan) - to outline a number of his concerns about the report and the conclusions outlined in the associated presentation material. The full report is available via the Global Maritime Hub.

Subsequently I obtained a copy of the aforementioned report that was prepared for Japan’s Ministry of Land, Infrastructure, Transport and Tourism (MLIT) and the presentation material entitled: Washwater discharge from open looped SOx scrubber system.

In the MLIT presentation it is stated that:

“Japan concluded that the discharge water with chemical substances such as SOx , PAHs and heavy metals can NOT cause unacceptable effects either on the marine organisms or on the seawater quality around Japan.”

That particular statement caught my attention as it is both vague (I.e. what is an unacceptable effect?) and in stark contrast to other reports that I had read.

For example in the published review paper: A New Perspective at the Ship-Air-Sea-Interface: The Environmental Impacts of Exhaust Gas Scrubber Discharge (2018) it is stated in the conclusions:

“there is incomplete understanding of the impact of scrubber wash water discharge on marine chemistry, biodiversity, and biogeochemical processes. In particular, there is limited information on the amount and composition of wash water discharge and the associated marine biological impacts.”


“We conclude that despite the existing guidelines for levels of monitoring and compliance of scrubber wash water, there is still the risk for acidification, eutrophication, and accumulation of pollutants in the marine environment, especially in the coastal regions”.

My initial assumption was that the research that had been conducted in Japan would clearly support the conclusions outlined in the MLIT presentation. However after reading the report by the expert board several times, I was unable to find clear evidence with the appropriate references to fully support those conclusions.

The report prepared for MLIT (or “Japan report”) is actually a collection of reports that were prepared by several universities, the National Maritime Research Institute (NMRI) and ClassNK. These individual reports are based on several studies regarding different aspects of open-loop scrubbers. For example one chapter is a theoretical study regarding the dilution rates of scrubber discharge water into the ocean using Computational Fluid Dynamics (CFD) analysis.

But this analysis is limited to a theoretical Panamax bulker operating at a constant speed of 12 knots and on a constant course. Dilution rates for different types of ships operating at slower speeds for example were not studied, nor was the dilution rate for a ship manoeuvring near an anchorage or berth. In addition the outlet for the discharge water was fixed at 1 metre below the waterline. No analysis was undertaken regarding situations when the outlet would be higher or lower as may be the case when the ship was unladen or laden for example. Another chapter was focused on the shore-based testing of just one open loop scrubber and no direct connection between the dilution rates and the shore based scrubber testing was established.

As I read through the report several more times I also found a number of statements that didn’t appear to be supported by the data and various assumptions appeared to limit the scope of what conclusions could be made. Therefore on the 16th May I submitted to MLIT a 6 page document in which I asked a number of questions and raised several concerns about the report including; why the dilution rate for only a ship operating at 12 knots was studied, why the sulphur content of the fuel used for scrubber testing was just 2.24%, and how could it be determined that scrubber discharge water would “Not cause unacceptable effects either on the marine organisms or on the seawater quality”? I also queried why no other studies from sources outside Japan related to scrubber discharge water were mentioned in the report. There was for example, no literature review as would typically be found in a research paper.

On the 6th of June I received a document from MLIT that contained responses to my questions and concerns. MLIT confirmed that there were some phrasing errors in the English version of the report due to the translation from Japanese. They also commented that the English version of the paper had not been peer reviewed, although the Japanese version had been reviewed by a panel of experts. In addition MLIT stated that the report was not a “usual academic research paper” and that it had been prepared as a background paper to help the Japanese Government with domestic policy.

The full list of questions & comments that I submitted to MLIT and their responses are contained in the document: Review of Ministry of Land, Infrastructure, Transport and Tourism (MLIT) Ship Scrubber Report and Presentation.

Many of the responses to my questions I feel should have been included in the original report. For example regarding my question as to why the scrubber discharge outlet was set to 1 metre below the waterline, MLIT commented it was not possible to simulate (the dilution rates) in detail for all ship types and that some modelling and approximation was inevitable. I agree, but I would also suggest that if a study only considers one ship type, operating at only one speed with the outlet at only one position that this is a fairly significant limitation.

Regarding fixing the ship speed at 12 knots, MLIT responded that it is the maximum speed limit in the concerned areas in Japan. In addition they stated that when a ship decreases speed, then the volume of the plume will decrease. Another limitation that would seem significant is that no discharge waste water was analysed from any ships fitted with scrubbers and samples were only taken from one type of scrubber tested ashore. MLIT explained that this was because no ships in Japan were fitted with open-loop scrubbers during the period when the research was conducted.

In my opinion that again is a fairly important limitation that would consequently reduce the scope of the conclusions that could be drawn. However on this and other points, MLIT does not agree.

In summary I would say the “Japan Report” is a useful body of work in terms of helping us understand what impact scrubber discharge water might have on the marine environment. However I believe it was premature for the MLIT to declare in their presentation that waste water from scrubbers “can NOT cause unacceptable effects” and, “.... Japan is of the position that there would NOT be a scientific justification to prohibit the use of open looped scrubber, as long as the IMO’s discharge criteria were met”.

With those conclusions in mind I will quote directly from the last paragraph contained in MLIT’s response to my questions:

“we do not agree to your comment that there are many important limiting factors/limitations in the study. We believe this study provides sufficiently reliable outcome based on best efforts within limited time and budget utilizing available information and technologies as of today.”

In conclusion please allow me to paraphrase a speech by Mark Antony from the immortal play Julius Caesar by William Shakespeare, I speak not to disprove what others spoke, but here I am to speak what I do know. In that context what I know is that the Japan report has been touted as research that settles the open loop scrubber debate.

In reality though it is a report that has limitations and contains some assumptions. I also know there is research available including the example that I cited earlier, that suggests we don’t know enough yet about scrubber discharge water to declare it safe. But I must stress that I am not saying or implying that open-loop scrubbers will cause harm to the marine environment.

That’s how it is in science sometimes, we just don’t have all the answers until further research is conducted and even then, there might be things we still don’t fully understand. So let’s hope that further research is conducted so that we get some more answers before shipping potentially scores an own goal & further damages its environmental reputation.

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